JPS63177124A - Projection exposing device - Google Patents

Abstract

PURPOSE:To increase the effective depth of focus of an exposure optical system regardless of the flattening of a substrate by composing projection light of plural light beams and providing such a function that respective conjugate image formation points for mask patterns of the plural light beams are near by a substrate and different on the same optical axis. CONSTITUTION:A light source 1 emits the composite light beam of light beams A and B which are linear polarized light beams. Both light beams are both incident on an auxiliary optical system 4 through a mask pattern on a mask 3 by an illumination optical system 2. The two light beams are split into two in the auxiliary optical system 4 through the diverging operation of a diverging element 7 and then incident on a projection optical system 5 through a converging element 8. The light beams A forms an image of the pattern on the mask 3 at a position 10 nearby the surface 9 of the substrate fixed on a substrate stage 6 through a projection optical system 5, and the light beam B, on the other hand, forms an image of the pattern at a position 11 different from the position 10 on the same optical axis, thus performing multiple image exposure. Consequently, the effective depth of focus of an exposure optical system increases.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a projection exposure apparatus used for forming fine patterns of semiconductor elements, magnetic bubble elements, superconducting elements, etc., for example.

[Conventional technology]

As is well known, projection exposure methods are widely used to form various fine patterns in semiconductor devices, magnetic bubble memory devices, and the like. Projection exposure methods, especially reduction projection exposure methods, are useful for forming extremely fine patterns, but in conventional projection exposure methods, the focus tolerance of the exposure optical system strongly depends on the numerical aperture of the projection lens and the exposure wavelength. was. The depth of focus of a projection lens is inversely proportional to the square of its numerical aperture and proportional to the exposure wavelength, so if you increase the numerical aperture or shorten the exposure wavelength to improve resolution, the depth of focus will decrease accordingly. becomes shallow. For this reason, it is becoming increasingly difficult to deal with obstacles caused by image plane distortion of the projection lens and irregularities on the surface of the substrate. Problems caused by steps caused by relatively fine patterns have been dealt with by smoothing using the well-known multilayer lens method. However, even if this method is used, it is not possible to completely flatten the level difference caused by the large-area pattern, and it is inevitable that poor imaging will occur in a portion or a lower part of the level difference.

Regarding the multilayer resist method, for example, please refer to the journal
of Vacuum Science and Technology,
Bee 1 (4), (1983) pp. 1235-12
40 pages (J, Vac, 'Sci.

"I'echno1. Bl (1983) pp i
235-1240), etc.

Furthermore, various types of reduction projection exposure apparatuses are known, such as Semiconductor World (Se
micoductor world )y 1984
It is shown in the July issue, pages 110-114.

[Problem that the invention seeks to solve]

As semiconductor integrated circuits have become more highly integrated in recent years, patterns have become finer, while the unevenness of the substrate surface has increased significantly, and measures to cope with these problems are required.

When a projection exposure method is used to form a pattern, the exposure optical system needs to have a larger depth of focus in order to cope with an increase in uneven steps. However, in order to improve the resolution, it is necessary to increase the numerical aperture of the projection lens as described above, so the depth of focus becomes shallower. Furthermore, because the image plane is not completely flat due to image plane distortion of the projection lens, it has become difficult to ensure a depth of focus corresponding to the unevenness of the surface over the entire exposure area.

Oij's multilayer lens method cannot completely flatten the irregularities of a large-area pattern, and even if complete flattening is achieved, the mask will be distorted due to the field distortion of the lens and the overall inclination of the substrate. The image plane of the pattern does not coincide with the substrate surface, making it difficult to deal with the above problem.

An object of the present invention is to provide a new device that can increase the effective depth of focus of an exposure optical system without relying on flattening the substrate. The objective is to cope with the decrease in focus latitude due to the increase in tilt, the numerical aperture of the projection lens, and the short wavelength of exposure light.

[Means for solving problems]

According to the inventor's study, the effective depth of focus of the exposure optical system is determined by multiple imaging exposure in which multiple images having the same mask pattern image plane at relatively different positions on the same optical axis J2 are superimposed. It has become clear that the increase can be achieved by doing this.

Therefore, the imaging planes of the same mask pattern are set at different positions on the same optical axis, and in order to achieve the above goal, we have developed a function that illuminates the mask pattern using multiple light beams, and a function that illuminates the mask pattern using multiple light beams. The reduction projection exposure apparatus is provided with a function of relatively diverging each of the light rays and dispersing them from each other. Each light beam dispersed by this function forms images at different positions on the same optical axis.

The above-mentioned diverging effect can be obtained, for example, by utilizing the birefringence phenomenon for two mutually orthogonal linearly polarized lights or the change in refractive index due to dispersion for light of different wavelengths.

[Effect]

In order to have good resolution of the pattern in the resist above and below the uneven steps on the substrate surface over the entire exposed area, the large-plane distortion of the projection lens, j! It is preferable that the light intensity contrast be maintained at a certain level within a certain range in the optical axis direction determined by the flatness of the plate and the height of the irregularities on the substrate surface. On the other hand, in the projection exposure method, the light intensity contrast for forming a pattern on the resist layer has a value that is sufficient to faithfully reflect the mask pattern near the imaging plane of the mask pattern (so-called depth of focus). range), and the contrast decreases rapidly as you move away from this range.

Therefore, when the depth of focus becomes shallow, it becomes impossible to maintain the necessary contrast within a range that requires a light intensity contrast 1- above a certain level, resulting in poor resolution.

Therefore, an attempt is made to superimpose a plurality of images of the same pattern having imaging planes at different positions within the range of the optical axis where a light intensity contrast of a certain level or higher is required. Figure 3a)
~C) are the images obtained by combining the images formed at the position Z = 1.5 μm on the optical axis, the image formed at Z = -1.5 μm, and the two images from the Book of Ju. The calculation results of the light intensity distribution are shown at several positions in the optical axis direction to illustrate the principle of the present invention. The pattern is assumed to be a hole pattern of 0.5 μm. As a result of the synthesis, a light intensity distribution effective for pattern formation is realized over a wider range in the optical axis direction than the light intensity above and below a single imaging plane.

In Fig. 3, the light intensity decreases as it moves away from the image plane.
approach. Therefore, as a result of overlapping, only the light intensity effective for pattern formation remains, but this property may be characteristic of isolated exposed portions in light shielding portions such as hole patterns. In more general patterns such as line and space, the light intensity distribution uniformly approaches a certain level as the distance from the image plane increases. Therefore, by superimposing this uniform light intensity distribution on a light intensity distribution effective for pattern formation, the contrast of light intensity generally decreases. but,
Again, the effective depth of focus increases.

Figure 4 shows the relationship between the position in the optical axis direction and the calculated value of the light intensity contrast of 0.7 μm line and space.
Each case of combining light with a point as an imaging point is shown below. In FIG. 4, the origin of the position in the optical axis direction is the center point of a single imaging point and two imaging points. As shown in Figure 4, by combining lights with different imaging points, the absolute value of the light intensity contrast generally decreases compared to the case of a single imaging point, but the contrast is maintained above a certain level over a wider area. I can see that it is being done. or.

By setting the distance between the two imaging points to an appropriate value, a constant light intensity contrast can be obtained within a certain range in the optical axis direction. The effective depth of focus increase rate depending on the method depends on the lens used, developer, contrast enhancement,
It is determined by the lower limit of the light intensity contrast 1 to 1 that can be resolved by the material and process. According to FIG. 4, the rate of increase in the effective depth of focus by using this method is when the distance between the two imaging points is 3.5 μm and the lower limit of the F light distribution intensity contrast is 0.5. While it is 45%, when the lower limit of the light intensity cons 1 to last is 0.4, it becomes about 70%. Further below, the limit is 0.
In the case of 3, the effective depth of focus is increased by 1.50% by superimposing three lights with different imaging planes. A contrast of 0.3 can be resolved in 1 minute using a CEL, and a contrast of 0.4 can be resolved using a TSS manufactured by Tokyo Ohka Co., Ltd.
Sufficient resolution can be achieved by using a resist with γ of 2.5 or more, such as M T < 8800.

For isolated exposed areas in light-shielding areas such as hole patterns, there is almost no drop in contrast l- due to overlapping, so by increasing the number of imaging planes set, the effective focal point can be virtually unlimited. Depth can be increased.

Main projection exposure device i? is equipped with a light source that emits several different types of light, and the mask pattern is irradiated with a composite light of the multiple types of light. Further, the present device includes an optical element that exhibits different refractive indexes for the plurality of types of light rays listed in item 11. The second optical element separates multiple types of different light beams into n. Here, the plural types of light rays may be, for example, light having different planes of polarization, or light having different wavelengths. These lights can each be separated by an optical element made of a double k11 folding ink or a material exhibiting a dispersion phenomenon.

The plurality of light beams that have passed through the mask pattern are separated from each other by the optical element (hereinafter referred to as a diverging element) that exhibits a different refractive index for each light beam, and then projected onto the substrate by a projection lens.

Therefore, the mask pattern is imaged at different positions on the same optical axis for each light beam. Therefore, according to this apparatus, exposure can be performed using a composite image of a plurality of images formed at different positions on the same optical axis. That is.

This device realizes multiple imaging exposure function. As already mentioned, this feature allows the light intensity contrast of the image to be maintained over a wider range in the beam direction, increasing the effective depth of focus.

〔Example〕

Example 1 FIG. 1 shows one embodiment of the present invention.

In the embodiment, as shown in FIG. 1, a light source 1. illumination optical system 2,
It consists of a mask 3, an auxiliary optical system 4, a projection optical system 5, a substrate stage 6, and other various components necessary for a normal projection exposure apparatus. The auxiliary optical system 4 includes a diverging element 7. Convergence element 8
It consists of These components are arranged as shown in FIG.

A light source 1 emits a composite light beam of light ray A shown by a solid line and light ray B shown by a broken line. Here, the light ray A and the light ray I3 are linearly polarized lights whose polarization planes are orthogonal to each other.

Both light beams are incident on the auxiliary optical system 4 by the illumination optical system 2 via the mask pattern of the mask 3''.

Within the auxiliary optical system 4, the two light beams are split into two by the divergent action (beam separation action) of the diverging element 7, and then enter the projection optical system 5 via the converging element 8. Projection optical system 5
Accordingly, the light beam A images the pattern on the mask 3 at a position 10 near the substrate surface 9 fixed on the substrate stage 6. On the other hand, light ray B traces the above pattern at position 1 on the same optical axis.
An image is formed at a position 11 separated by a distance Δ from 0. However, the distance Δ is set within the range given by the following equation based on the exposure wavelength λ and the numerical aperture NA of the projection lens. That is.

λ Ohm≦3 The diverging element 7 used here is composed of a glass concave lens and a crystal plano-concave lens. The refractive index of both rays for glass and the refractive index of ray A for crystal are equal. On the other hand, the refractive index of the light ray B for the crystal is larger than that for the light ray.

Therefore, this diverging element acts as a flat glass plate for the light AWA, but acts as a concave lens for the light ray B.

Therefore, it has the function of making the light ray B diverge from the light ray A. On the other hand, the converging element is composed of a plano-concave lens made of the same glass material and a quartz plano-convex lens, and acts as a flat glass plate for light ray A, but acts as a convex lens for light ray B. Therefore, it has the function of converging the light ray B that has diverged from the light ray A into a light ray again. As for the structure of the diverging element and the converging element, various methods other than those shown here are possible. Also, a diverging element.

The converging element does not have to act as a concave lens and a convex lens only for the ray 3 as shown here, but may exhibit a refractive effect for both rays.

It is necessary to equalize the magnification of the mask pattern at the imaging positions 10 and 11 of the mask pattern by the light rays A and B, respectively. For this purpose, it is necessary to converge the light rays A and B, which have been relatively diverged by the diverging element 7, by the converging element 8, so that the intersection of the two light rays coincides with the focal point of the projection optical system 5 on the mask side. The arrangement of pixel elements is determined by performing ray tracing that satisfies the above conditions.

Further, the positions of the diverging element 7 and the converging element 8 can be adjusted within the above-mentioned allowable range of Δ while making the intersection point of both light rays coincide with the mask-side focal point of the projection optical system 5. This results in 2
The distance Δ between two images can be changed depending on the mask pattern. Note that if the diverging element 7 itself can be placed accurately at the mask-side focal position of the projection optical system 5, the converging element 8
The magnification of the mask pattern at the two imaging positions can be made equal without using. However, in this case, the distance Δ between the two imaging points cannot be adjusted. As described above, there is an optimum value for the imaging point distance Δ depending on the mask pattern. Table 1 shows examples of preferable values of Δ for various patterns when a projection lens with N, A = 0.42 and exposure light with a wavelength of 365 nm are used. These values are within the setting range of Δ described above.

With the above functions, resist is applied to two different points on the same optical axis separated by a distance equal to or less than the depth of focus of the projected image of the mask pattern using the same magnification unit. The substrate stage was exposed to light at various heights, and then developed to form a resist pattern. At this time, the range of the substrate stage height in which the pattern is resolved becomes the focus latitude of that pattern.

The numerical aperture of the projection optical system used was 0.42, and the exposure wavelength was 365'nm. The exposed pattern is a hole pattern with a diameter of 0.5 μm, a line and space pattern with a line width of 0.5 μm, etc. first.

When exposure was performed by adjusting the positions of the diverging element 7 and the converging element 8 and setting the distance Δ between the two imaging points to 2 μm, the result was 0.
．． Focus tolerance for 5μm diameter hole pattern is ±1.5μ
It turned out that m. Further, when exposure was carried out with the pixel element positioned on the optical axis and Δ=4 μm, the focus latitude of the pattern was ±μm. Also, line width 0.5μ
Almost similar results were obtained for the m line and space pattern.

On the other hand, with conventional exposure equipment using the same projection lens and exposure wavelength, the focus tolerance for these patterns is ±
Only 1 μm or less was obtained.

The projection lens of this device has an image field distortion of 1.0 μm in width, and the substrate used has approximately 1.
There is an effective step difference of μm. Therefore, even if there are no steps at all on the substrate surface, it has been impossible for the conventional apparatus to resolve the above-mentioned pattern over the entire exposed area. but,
By using this device, this has become possible even when a step with a height of 2 μm exists on the substrate surface. This results in
It has become possible to apply optical lithography to the manufacture of 0.5 μm rule devices.

Further, using this apparatus, the same mask pattern was exposed at the same position on the substrate, and the height of the substrate stage was changed by only twice the distance Δ between the image forming points. As a result, the focus tolerance of the 0.5μm hole pattern was further doubled (four times the conventional method) by ±4.
It was possible to make it μm. Furthermore, the stage height is increased by 2Δ
By performing overlapping exposure 0 times with a shift in steps, the focus latitude could be increased by 2n times that of the conventional method.

Note that the cross-section of the pattern depended on the type and size of the mask pattern, and the materials and processes used for the resist, etc. In general, for patterns such as line and spaces, if multiple imaging exposure is performed using this device, the sharpness of the cross section of the resist pattern will be lost, so it is preferable to use the CEL method or high γ resist process in combination. . However, in the case of a hole pattern, no deterioration of the pattern shape was observed even when the multiple imaging exposure method was applied using this device. Instead of polarized light, we used light beams with two different wavelengths.

Along with this, the material of the diverging element and the converging element was changed to a substance that exhibits a birefringence phenomenon, and the optics other than the six-shot element and the converging element were changed to a substance that exhibits a different refractive index due to a dispersion phenomenon for the two wavelengths. As the constituent materials of the element, we selected materials that do not exhibit a significant fractional polarization phenomenon with respect to the two wavelengths.

Two light sources were provided in order to combine two light beams having different wavelengths, different wavelengths were selected for each of them using filters, and these were combined using a half mirror or the like. Of course, the light emitted from one light source can be divided into two by using a half mirror.
It is also possible to separate them into parts and pass different wavelengths through each of them, or to pass them through a filter and then combine them again using a half mirror.

Experiments similar to those in Example 1 were conducted using this device, and similar effects were obtained.

Example 3 FIG. 2 shows another embodiment of the invention.

This device uses excimer laser beams A with different wavelengths.
, B, and various components similar to those shown in the first embodiment. Two laser beams emitted from each light source are combined by a half mirror 103, and an image is formed by an illumination optical system 104 on the entrance pupil of a projection optical system 107 via a mask pattern on a mask 5 and an auxiliary optical system 106. . Laser beams A and B that have passed through the mask 105 are used to form a mask pattern on the mask 105 at two different points 109 and 110 on the same optical axis near the substrate surface 108 using an auxiliary optical system 106 and a projection optical system 107, as in the first embodiment. Each image is formed.

Illumination optical system 104. All refractive optical systems including the projection optical system 107 are made of quartz-based materials that have low absorption of excimer lasers. This material exhibits different refractive indexes for the two laser beams A and B due to the dispersion phenomenon. It is possible to separate both light beams and image them at different positions on the same optical axis. However, since the illumination optical system 104 and the projection optical system 107 also have a diverging effect on both light beams,
The configuration of all optical systems is slightly more complicated than that of the first embodiment.

First, two light sources 101 and 102 and a half mirror 103 are used to form an equal image of both light beams having different refractive indexes on the entrance pupil of the projection optical system 107 for the illumination optical system 104.
I had to adjust the distance between them.

The auxiliary optical system 106 is composed of a diverging element 111 and a converging element 112 as in the first embodiment. As mentioned above, the projection optical system 10
It goes without saying that the arrangement conditions of the diverging element 111 and the converging element 112 are different from those in Example 1 since the dispersing element 7 itself has a diverging effect on both the light beams.
1. There is no particular need to distinguish the converging element 112 from the projection optical system 107. Furthermore, if the magnification error of the projected image due to both light beams can be ignored, only the beam separation effect of the projection optical system itself may be used without providing a diverging element and a converging element.

2 shows different dispersion and sufficient transmittance for two wavelengths.
When more than one type of substance can be used, it is preferable to use them in combination. For example, in addition to quartz glass, fluorite or the like may be used in combination.

The two light sources shown in this embodiment may be other than an excimer laser light source, such as a normal ultraviolet light source equipped with a filter for selecting an appropriate wavelength. In this case, it goes without saying that restrictions on various refractive optical system components are significantly reduced.

Using this device, an experiment similar to the first example was conducted and similar effects were confirmed.

〔Effect of the invention〕

As is clear from the above description, by using the present invention, it is possible to increase the effective depth of focus in the projection exposure method, thereby increasing the numerical aperture of the projection lens, shortening the wavelength of the exposure light,
It is possible to cope with the image plane distortion of the projection lens and the increase in the sloping unevenness of the substrate surface. By applying the present invention and a high contrast resist process such as the CEL method, the effective depth of focus of a submicron pattern can be increased by approximately 70 to 100% when the number of set images is two compared to the conventional method. Can be done. Therefore, for example, 2μ on the substrate surface.
Even when there is a height difference of m or more, the field distortion of the lens,
It was possible to resolve a pattern of 0.5 μm or less over the entire surface of the n-light region without making any special improvements to the degree of inclination of the substrate.

As a result, in the past, it was virtually impossible to apply optical lithography to the manufacturing of LSIs with a line width of 0.5 μm due to lack of focus latitude, but by adopting the present invention, this can be improved to 80 μm. It has become possible to perform this process with a yield of over 30%.

Furthermore, recently, excimer lasers have been attracting attention as a next-generation light source for optical lithography, but when this is used, the exposure wavelength becomes even shorter and the focus latitude is further reduced.

Therefore, the present invention is very effective as a technology for utilizing excimer lasers.

[Brief explanation of the drawing]

1 and 2 are diagrams showing different embodiments of the present invention, FIG. 3 is a schematic diagram for explaining the present invention in detail, and FIG. 4 is a curve diagram showing the effects of the present invention. It is. 1... Light source, 2... Illumination optical system, 3... Mask,
4... Auxiliary optical system, 5... Projection optical system, 6... Substrate stage, 7... Diverging element, 8... Converging element, 9
... Substrate surface, 10... Image formation position of light ray A, 11.
...Image position of ray B, A... ray, B... ray. 101.102...Excimer laser light source. 103...Half mirror-1104...Illumination optical system,
105...Mask, 106...Auxiliary optical system, 107
...Projection optical system, 108...Substrate surface, 109...
Image formation position of laser A, 110...image formation position of laser B. 111...divergent element, 112...convergent element. 1 piece 2
Rain 3 sides a) b) , c) vJ q En-ll -6-4-:2 θ 2 Gu 68
t-71′″ Hyakuryo t

Claims (1)

[Claims] 1. In a projection exposure apparatus that projects and exposes a mask pattern onto a substrate, the projection light is composed of a plurality of light rays, and the conjugate imaging points of the plurality of light rays with respect to the mask pattern are near the substrate and at the same point. A projection exposure apparatus characterized by having a function of forming different points on an optical axis. 2. The function of focusing each of the plurality of light rays on different points on the same optical axis near the substrate is to relatively diverge each of the plurality of light rays that have passed through the mask pattern due to the difference in refraction angle. 2. The projection exposure apparatus according to claim 1, wherein the projection exposure apparatus has a combination of a function of separating the separated light beams and a function of focusing each of the separated light beams on different points on the same optical axis near the substrate. 3. The shortest distance Δ between different imaging points on the same optical axis is in the range of Δ=m{λ/(NA＾2)}, where 0<m≦3. A projection exposure apparatus according to scope 1. 4. The projection exposure apparatus according to claim 1, wherein the plurality of light rays are two types of light rays. 5. A patent characterized in that the plurality of light rays are two linearly polarized lights perpendicular to each other, and the function of relatively diverging each of the plurality of light rays is performed by an element made of a material having birefringence characteristics. A projection exposure apparatus according to claim 2. 6. The plurality of light rays are light rays having a plurality of different wavelengths, and the function of relatively diverging each of the plurality of light rays is a dispersion characteristic in which the function of relatively diverging each of the plurality of light rays shows a different refractive index for the light having each of the wavelengths. 3. A projection exposure apparatus according to claim 2, characterized in that the projection exposure apparatus is carried out by an element made of a material having .